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5. Tick the correct answer in the following and justify your choice : If the perimeter and the area of a circle are numerically equal, then the radius of the circle is

                (A)    2 units
                (B)    \pi units
                (C)    4 units
                (D)    7 units

Let the radius of circle be r. Then according to question, we can write :-                              Perimeter      =     Area                                     Hence option (A) is correct.

4. The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is travelling at a speed of 66 km per hour?

Let the number of revolution of the wheel be n. The circumference of the wheel is given by:-                                                                                   Now, the speed of the car is given by:-                 Thus distance travelled in 10 minutes is:  According to the question, we get:;                                          or                                         ...

3.  Fig. depicts an archery target marked with its five scoring regions from the centre outwards as Gold, Red, Blue, Black and White. The diameter of the region representing Gold score is 21 cm and each of the other bands is 10.5 cm wide. Find the area of each of the five scoring regions.

                                                         

Radius of each scoring region can be found by adding 10.5 in respective colours. The area of golden region is :       Similarly area of the red region is   =   Area of red score  -  Area of golden region                                                        Then area of blue region is :                                                      And area of the black region is :                    ...

2. The radii of two circles are 8 cm and 6 cm respectively. Find the radius of the circle having area equal to the sum of the areas of the two circles.

We know that the area of the circle is   :     Thus area of a 1st circle  :     or                                        And the area of a 2nd circle is   :   or                                          According to the question area of the new circle is    or                                            or                                               Hence the area of the new circle is 10 cm.

1. The radii of two circles are 19 cm and 9 cm respectively. Find the radius of the circle which has circumference equal to the sum of the circumferences of the two circles.

Circumference of 1st circle is given :                                                                      And cicumference of 2nd circle is :       Thus the circumference of the new circle is    or                       or                      Hence the radius of the new circle is 28 cm.
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